Organic polymers must have a high softening point, e.g., a high glass transition temperature (Tg) to retain adequate mechanical properties for a useful lifetime at expected service temperatures. Prior art composites prepared from stoichiometrically balanced aromatic polyimide precursors and reinforcing substrates while theoretically affording the highest glass transition temperatures, have a void level that adversely affects mechanical properties and specifically compression properties. To ameliorate the problem various techniques have been employed, some of which require additional or more costly processing steps. The use of monomeric or low molecular weight prepolymer solutions facilitates impregnation of fiber structures, however, it still remains difficult to complete polymerization and devolatilization with the "wet" prepreg while achieving essentially complete consolidation, or compaction. This, in turn, has made it difficult to routinely produce high quality, low void, composite laminates with such resins, especially using the low to moderate pressure autoclaves which are typical of the aerospace industry composite manufacturing capability. The present invention is a new technique for achieving this objective in a simple manner.